I put together two clear plastic lures boxes like the ones used for fishing........24 compartments in each box.
Next I bought-- in kits and seperately all the PINS and SPRINGS found in the AR15. Added to that mix you want a firing pin, some gas rings (3), some ejectors, one or two extractors, a hammer and a trigger group.
I also bought a buffer retaining pin and the long pin that holds the ejection port door.
Also I bought a spare Gas Key for the Bolt with 2 -screws that attaches it. I also bought a spare Gas tube ($10) for the size barrel I have.
Ideally you would want a spare bolt to go with these kits.........I haven't bought that yet.
I have spent to date about $100 on everything ( not counting the bolt )
Now I don't have to worry about loosing a pin or tiny spring.........I always have a spare. It was fun building the kits and labeling each compartment. If anyone is interested I can try and take a photo of both plastic boxes ??
JF.